The invention relates to a device for discharging bulk material from a store thereof. The bulk material comprises solid material divided into small particles, such as grains, powder or the like. The bulk material does not flow easily by itself but must be provided with some mechanical aid. Examples of bulk material with which the invention is particularly suited include wood chips, corn, sand, and coal.
In the past, discharging of bulk material from a store thereof is rarely accomplished uniformly. Rather, different horizontal layers of the bulk material become intermixed. The intermixing of layers, and the existence of some of the stored material in a storage vessel for significantly longer periods of time than the average material, has many disadvantages when the bulk material is ultimately utilized.
In one form of prior art device, a rotatable drum is provided having an end portion thereof mounted for rotational movement about an axis substantially at the center of the store of bulk material. The drum has teeth and openings evenly distributed along the length thereof. As the central part of the bottom of the bulk material is acted upon by more teeth in a given period of time than the peripheral locations of the bulk material, the material in the store will descend more quickly, forming a funnel shaped depression in the surface of the material. The bulk material at the periphery will fall into the funnel shaped depression so that the strata will be intermixed, no uniform descent being provided.
In another form of prior art device, the bulk material is stored in a silo having walls that are inclined upwardly, with a horizontally traversable screw conveyor mounted at the bottom of the silo. Even descent of the material over the cross-section of the silo is not achieved since near the discharge end of the screw its threads will be completely filled with material that has entered the screw at the fore end of the screw. Material at the fore end of the screw will thus descend more quickly than at the discharge end, again resulting in non-uniform descent and intermixing of strata.
According to the present invention, a device for discharging bulk material from a store is provided that provides for uniform descent of the bulk material from the store, no intermixing of layers taking place. Such a device includes a rotary screw conveyor rotatable about a longitudinal axis and surrounded by an elongated drum which is rotatable independently of the screw conveyor and which is provided with inlet apertures distributed over the periphery and along the length of the cylindrical face of the drum. Means are provided for mounting the rotary screw conveyor and drum for movement in a straight path perpendicular to the longitudinal axis of the rotary screw, and means are provided for powering the conveyor and drum in that longitudinal path. Further, means for effecting rotation of the rotary screw conveyor in the drum are provided so that the drum apertures during the combined rotation and linear displacement thereof dig into the layer of bulk material and transfer the material into the drum to be displaced by the screw conveyor so that the desired uniform descent of the bulk material from the store takes place. The inlet apertures may be shaped as axially or obliquely extending slits, with slits situated in the same cross-section of the drum equally spaced in the peripheral direction, and with at least one inlet aperture in each cross-section of the drum except at its outermost ends.
During long periods of non-use of the discharging device, a detrimental deflection of the drum may take place due to the settling and compaction of the bulk material. The drum, which usually "floats" in the bulk material during normal operation, does not do so during long stand-stills since the material does not engulf the undersurface of the drum. Without bulk material on the undersurface of the drum transmitting pressure thereto, the pressure of the bulk material above the drum causes excessive deflection thereof; this deflection may result in binding of the drum so that it will not properly rotate when start-up is attempted, resulting in damage thereto. Additionally, too great a deflection may permanently warp the drum.
According to the present invention, means are provided for preventing detrimental deflection of the drum during long periods of non-use due to settling and compaction of the bulk material, while not interferring with movement of the drum in its straight line path during use, and facilitating rotation of the drum during start-up after a long period of non-use. Such detrimental deflection preventing means preferably comprise a metal rail mounted in the floor over which the drum and conveyor move, and generally extending in said straight path, with a top surface substantially flush with the floor. A block of low friction material (such as a high-molecular plastic material like Teflon) is operatively connected to the rail, extending along the entire upper surface thereof, and upstanding therefrom a distance less than the spacing of the drum from the floor during rotation of the drum. A single rail and block preferably are provided located adjacent the axial midpoint of the drum and extending perpendicular to the direction of elongation of the drum so that the drum makes line contact with the block when deflected into contact therewith over long periods of non-use.
Additionally, according to the present invention means are provided for counteracting any tendency of the bulk material to wedge in the spacing between the drum and the block, thereby lifting the drum. Such counteracting means preferably comprises a helical strip of steel having a total axial dimension at least as great as the width of the block, with means for mounting the strip on the drum so that a part of the strip always lies closely above the block and during rotation of the drum an edge of the strip sweeps bulk material sideways off the block. When the drum includes eyelids formed bordering at least some of the inlet apertures extending radially outwardly from the drum, the strip is dimensioned so that it is at least as thick as the distance the eyelids radially outwardly extend from the drum. The apertures are preferably rhomboid in shape and have centers equidistantly located on one or more helical lines extending parallel to the helical strip with the strips spaced from the apertures. In a preferred embodiment, a lowermost portion of the strip is vertically spaced from an uppermost surface of the block a distance of about 50 mm during rotation of the drum.
It is the primary of the present invention to provide a device for effecting uniform descent of bulk material from a store, without detrimental effect after long periods of non-use. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.